1. Field of Invention
The invention relates to a method for the diagnosis of tuberculosis, especially bovine tuberculosis, by both cellular immune response detection and antibody detection assays in animals including human beings.
2. Description of Related Art
Tuberculosis is caused by Mycobacteria belonging to the Mycobacteria tuberculosis complex group (MTC), which comprises Mycobacterium tuberculosis (M. tuberculosis), Mycobacterium bovis (M. bovis), Mycobacterium caprae (M. caprae), Mycobacterium africanum (M. africanum), Mycobacterium microti (M. microti) and Mycobacterium pinnipedii. 
In methods addressed to by the invention, samples, especially blood samples from a human or an animal are analysed for the presence of a cell-mediated immune response to mycobacterial antigens or of mycobacterial antibodies, respectively, and the presence of a cell-mediated immune response or of antibodies is taken as indication for tuberculosis.
Known methods comprise incubating a blood sample from an animal with mycobacterial antigens, and detecting the presence of cell-mediated immune-response resulting from the incubation or detecting antibodies to mycobacterial antigens, respectively.
EP 0 296 158 discloses a method for the diagnosis of infections including tuberculosis in samples from human or animals. In a first step a whole blood sample from a possibly infected human or animal is incubated with antigens, e.g. a purified tuberculin protein derivative (PPD). After incubation the sample is analysed for the presence of interferon gamma (IFN-γ) released by sensitised lymphocytes to indicate a cell-mediated immune response to the antigen.
PPD has a high sensitivity, its specificity, however, is limited. Therefore, efforts were made to identify further tuberculosis test reagents suited for
EP 0 408 625 discloses antibody and cellular assays which use MPB-70 protein from Mycobacterium bovis as antigen.
Pub. No. US 2006/0115847 and WO 2006/117538 disclose different peptides, which can be used as antigens in cellular assays and which are mainly selected for their property to distinguish between tuberculosis infection and vaccination with BCG strain.
Finally EP 0 706 571 discloses the use of an antigen called ESAT-6 and WO2004/099771 the use of an antigen called CFP-10 in assays for the diagnosis of tuberculosis.
ESAT-6 and CFP-10 are so far the most immunogenic antigens with superior specificity compared to PPD stimulating in vitro IFN-γ production by T-cells. However, cross-reactivity with Mycobacterium kansasii (M. kansasii) occurs as ESAT-6 and CFP-10 genes of M. bovis and M. kansasii are highly identical. M. kansasii, not included in the MTC, may be isolated from healthy as well as rarely from diseased individuals and cattle. Management of tuberculosis is often complicated by false interpretation of tests presumptive for MTC.
It has turned out, however that different antigens detect a partially differing population of tuberculosis infected animals. The sensitivity of these antigens appears lower than the sensitivity of tuberculin. As a consequence in some situations, assays using the antigens can produce false negative results.
In view of the above it is an object of the invention to provide an antigen which allows the design of methods for the diagnosis of tuberculosis with increased specificity and, eventually in combination with other antigens, with increased sensitivity.